A primary consideration in the design and construction of vertical conveyance equipment, such as an elevator system, resides in the safety of operation of the system. Accordingly, a reliable braking system for an elevator system that can effectively stop and hold the elevator car in case of power loss, mechanical or electrical malfunction or other emergency is critical. Strict governmental regulations regarding the safety of elevator systems are therefore widespread. Braking systems in use have employed various mechanical, electrical or magnetic devices for accomplishing effective braking control for the elevator. One such device is a clamp type rail brake that grips a guide rail wherein pressure of the braking surfaces is produced by spring force, and is often used as a safety brake to stop an elevator platform in case of excessive upward or downward speed. Other braking systems have used drum brakes and disk brakes that engage the drive shaft of the elevator motor, or spring-biased brake shoes acting on the elevator traction sheave or hoisting cables, or clamp type brakes in elevators with linear motors, or incorporating electromagnetic holding elements. Some examples of elevator brake mechanisms may be found by reference to U.S. Pat. No. 4,923,055 to Holland, U.S. Pat. No. 5,007,505 to Lindegger, U.S. Pat. No. 5,202,539 to Lamb, U.S. Pat. No. 5,495,919 to Ericson et al, U.S. Pat. No. 5,518,087 to Hwang et al, U.S. Pat. No. 5,669,469 to Ericson et al, U.S. Pat. No. 5,717,174 to Ramos, U.S. Pat. No. 6,131,704 to Viita-Aho et al, U.S. Pat. No. 6,374,964 to Mustalahti et al, U.S. Pat. No. 6,675,939 to Maurice et al, U.S. Pat. No. 7,036,638 to Simmonds et al, U.S. Pat. No. RE36,034 to Sheridan, and U.S. Patent Pub 2008/0264727 by Mustalahti et al (the disclosures of all of which are incorporated herein by reference).
A common characteristic among conventional elevator braking systems, including those just referenced, is that the holding mechanism typically involves friction between the elements of each braking system and the supporting structures or the driving mechanisms of the elevator system. Additionally, many prior art braking systems operate only for elevator motion in the downward direction.